WEBVTT 00:00.000 --> 00:07.000 This is Hacker Public Radio episode 34 for Thursday 6 February 2020. 00:07.000 --> 00:13.000 Today's show is entitled Fixing Simple Audio Problems with Audacity. 00:13.000 --> 00:18.000 It is hosted by Dave Morris and is about 13 minutes long 00:18.000 --> 00:22.000 and carries an explicit flag. The summer is 00:22.000 --> 00:27.000 sharing a few experiences with Audacity that may be helpful to others. 00:27.000 --> 00:32.000 This episode of HPR is brought to you by AnanasToast.com. 00:32.000 --> 00:38.000 Get 15% discount on all shared hosting with the offer code HPR-15. 00:38.000 --> 00:40.000 That's HPR-15. 00:40.000 --> 01:07.000 Better web hosting that's Aniston Fair at AnanasToast.com. 01:11.000 --> 01:30.000 Hello everybody, this is Dave Morris and I'm welcoming you to Hacker Public Radio. 01:30.000 --> 01:41.000 Today I want to do a brief show talking about using Audacity to solve a few audio problems. 01:41.000 --> 01:43.000 I'm no expert on the use of Audacity. 01:43.000 --> 01:47.000 I have a bit of experience and have managed to fix a few things. 01:47.000 --> 01:53.000 But I thought in sharing a few recent experiences might be helpful to others. 01:53.000 --> 02:01.000 Maybe get a conversation going and get some more contributions to this subject from people who perhaps know a lot more than I do. 02:01.000 --> 02:08.000 What happened was I recorded the audio for a show I did with Mr. X in 2019. 02:08.000 --> 02:12.000 Number 2972 it was. 02:12.000 --> 02:18.000 We were setting my car because it could not be very quiet and it was very cold so you don't want to be outside. 02:18.000 --> 02:27.000 And I used my zoom H2N recorder when I'm using now actually and I put it on a little tripod on the dashboard of my car. 02:27.000 --> 02:40.000 But something about this setup caused to me anyway the resulting audio to be very sort of boomy and echoey and quite a lot of sort of bassiness in it. 02:40.000 --> 02:54.000 And I was keen to reduce that make it a little less unpleasant to listen to. Now one of the things that I do with pretty much all of my audio. 02:54.000 --> 03:12.000 I'm not only because I when I'm speaking when I'm doing these types of things I tend to have a not a script so much. I tend to be looking at the notes that I've prepared already and I tend to be sort of riffing riffing on them. 03:12.000 --> 03:35.000 Along the way I sort of hesitate and leave gaps so I thought I usually run truncate the truncate silence effect in audacity to clean that stuff up but I have not been doing this very well I feel because listening back some of the results. 03:35.000 --> 04:00.000 And here that if you speak of I do where you sort of try a little bit very quiet towards the end of the sentence the truncate silence just chops that off and if you don't start a word very loudly then it can also do the same and you do hear on others other stuff as well and it is a common issue with the silence truncation I think. 04:00.000 --> 04:09.000 I thought in this particular case I would try and get truncate silence to work better or learn how to use it better. 04:09.000 --> 04:21.000 So put a couple of requests in the notes here if I didn't do a good job explaining all this stuff in this show then let me know and tell me what I should have done. 04:21.000 --> 04:31.000 And if you have the expertise then how about doing an HBR show to talk about how you deal with common audio problems. 04:31.000 --> 04:49.000 For example I've had things where there's a mains hum probably because where I record in the proximity of I mean my sort of dining kitchen area and there's things like fridge freezes to actually quite close by so I think sometimes mains hum gets into stuff. 04:49.000 --> 04:59.000 So how would you remove that and do you use compression and normalization to clean things up? That's a good thing would be amazing to know more about I feel. 04:59.000 --> 05:18.000 So what did I do with the audio of this episode 2972? Well the first thing I did and I always do is to run the noise reduction effect and that's because most of what I produce has some background noise. 05:18.000 --> 05:33.000 And I need to to chop that out. Well I have to do is to select the effect and sample a piece of the audio to get what they call a noise profile. 05:33.000 --> 05:44.000 What I do usually is to get set the switch to the recorder on let it run for a little while a few seconds. So I've got a sample of noise to do this with. 05:44.000 --> 06:06.000 And then having taught the effect what the noise profile looks like then I select the whole thing tune settings a bit and run it on the whole thing and you should see the silences that the amount of noise in the silences disappearing somewhat. 06:06.000 --> 06:16.000 So that's that's thing I find is really really useful to do. I'm not going to go in a lot of detail about how you do this because if you're going to look at the audacity manual and I've linked it. 06:16.000 --> 06:29.000 It shows diagrams and explains it really really well much better than I can do. So the second thing I did was I ran a high pass filter on the audio. 06:29.000 --> 06:48.000 Now this is a way of reducing low frequency noise and as I said before I felt that there was the hollow nature of the original audio was perhaps due to the audio frequencies that are knocking about inside my car. 06:48.000 --> 07:01.000 It wasn't damped properly or something. I really don't fully understand somebody who's a proper audio engineer might be able to explain why it would be like that. There's only other people recording their cars and it doesn't sound too bad. 07:01.000 --> 07:19.000 Anyway, I thought how about if I remove if I try a high pass filter and what this does, it passes the frequencies above a certain threshold that you set and attenuate frequencies below that cut off frequency. 07:19.000 --> 07:42.000 I set the cut off frequency to 500 Hz and there's a roll off setting which is the decibels per octave to 6 decibels. I had tried what the effect offered me as the default which was a 1000 Hz in the first instance but it was awful. 07:42.000 --> 07:58.000 So I think it actually removed much of much of it. It doesn't really sound like a human speech at all. So 500 seemed to be a good compromise and that seemed to do something useful. 07:58.000 --> 08:24.000 It did, you could hear to me anyway, you could hear the reduction of some of the frequencies. It seemed to me to take away that sort of weird boomingness. Now because that high pass filter reduced the overall volume, I then applied an amplification pass and this is quite well documented and it felt easy to do. 08:24.000 --> 08:43.000 There's a value in the amplification box when you fire up this effect and if you follow that it will produce a new peak amplitude of zero decibels, which is sort of normal level, I guess you'd say. 08:43.000 --> 09:03.000 And in the case where I did this, the value was 1.106 decibels. So I just use that because you can do these things, you can run the effects, listen to what the result is and then click undo, you can experiment. 09:03.000 --> 09:17.000 Especially if you make sure you've saved the work so far before you do it. I might not have amplified it quite enough because the end results sounded moderately quiet when listening to it on HPR. 09:17.000 --> 09:41.000 The widely it sounded fine when played through audacity, but obviously the settings are different in the two situations. Anyway, it bumped things up a little bit more so it didn't sound quite so faint after this, the work already done on the sound. Then came these silence truncation, which I tend to do at the end of everything. 09:41.000 --> 09:51.000 This sort of order I normally use, if I'm doing this sort of stuff, which again I'm open to to comment on, it doesn't seem like I'm doing this right. 09:51.000 --> 10:06.000 So as I said in the notes, there's an art to using silence truncation, and I said in the preamble that the effects it has, if not used correctly, is that it chops the beginnings and ends off words. 10:06.000 --> 10:19.000 When I started doing this on this particular audio, I did it the way I normally do it, and there were some really unpleasant truncations applied to it. 10:19.000 --> 10:46.000 So this may be one of going experiment with how to do a better job. The truncate silence effect is documented really well, so I've referred to that. When I did was I set the threshold to minus 25 decibels. I tried using minus 20, but that caused some of the quieter sounds of words to get truncated. 10:46.000 --> 10:59.000 So the decibel scale is logarithmic and zero is sort of the normal, the mean I guess, and so it'll probably explain it better in the audacity manual. 10:59.000 --> 11:14.000 Anyway, I use minus 25 decibels. Then I went for a duration of half a second, 0.5 seconds, I used the compress excess silence option, and 11:14.000 --> 11:25.000 shows compressed to 50%. You'll see this in the documentation. Now this is the first time I'd use this combination of settings. 11:25.000 --> 11:34.000 Previously I'd chosen the truncate-tected silence option, and had not been using the best threshold value to do it. 11:34.000 --> 11:49.000 So I think that the end result is a lot better. It's not quite a brutal with removal, so if you've got a long piece of audio with sounds as in it, it doesn't reduce it quite as much as the other one would. 11:49.000 --> 12:04.000 However, the end result sounds a lot nicer. The end result sounded pretty good, and I'm hoping that this will help people to, if they're not doing something like this, to have a go at it, if the mood takes them. 12:04.000 --> 12:25.000 So what I'm going to do is to play the same chunk of audio from the show I've been talking about, and with the different effects. So the first one is the original audio, as it came off the recorder. 12:25.000 --> 12:37.000 It's got noise in it. I think it sounds boomy, but more I look at this the less I'm convinced. However, I'm hosting anyway. So here it is. 12:37.000 --> 13:06.000 Everybody, this is Hacker Public Radio, welcome to our show. So the next one is after noise reduction, doing the same sort of thing as I mentioned before. I haven't taken the noise from this piece of audio itself, but from the preamble in front of it, to have included. So just if you can see the waveform, you'd see that it's a lot cleaner. 13:06.000 --> 13:23.000 Everybody, this is Hacker Public Radio, welcome to our show. Next is the high pass, sort of doing the high pass filtering, and it's, you can hear it's, it's got a lot more. 13:23.000 --> 13:38.000 That's like an old fashioned telephone in some respects, the number of frequencies have been reduced, you can tell that. And from the waveform, you can see that stuff has been reduced, a piece of been reduced in height, which is why. 13:38.000 --> 13:59.000 Everybody, this is Hacker Public Radio, welcome to our show. The next one, I have thought that the volume was too low, sort of amplified things, and this is the result, waveform looks a lot higher than the previous one. 13:59.000 --> 14:12.000 Everybody, this is Hacker Public Radio, welcome to our show. And the last one has had some sound instruction, there wasn't much silence in this sample. 14:12.000 --> 14:33.000 We were, there were two of us talking, so whenever there was a gap somebody else spoke, so there wasn't a lot to remove, however, I wanted to demonstrate that it's possible to do sound instruction without nibbling away at the starts and ends words. So that's the end product. 14:33.000 --> 14:51.000 Everybody, this is Hacker Public Radio, welcome to our show. So hopefully that demonstration helps a wee bit, I hope you found it entertaining, even though you had the same clip over and over and over. I got bored, so you probably got a little bit. 14:51.000 --> 14:53.000 Okay, that's it then, bye-bye. 14:53.000 --> 15:03.000 You've been listening to Hacker Public Radio as Hacker Public Radio.org. 15:03.000 --> 15:09.000 We are a community podcast network that releases shows every weekday Monday through Friday. 15:09.000 --> 15:21.000 Today's show, like all our shows, was contributed by a HPR listener like yourself, if you ever thought of recording a podcast and click on our contributing to find out how easy it really is. 15:21.000 --> 15:30.000 Hacker Public Radio was found by the digital.com and the Informamican Computer Club and it's part of the binary revolution at binref.com. 15:30.000 --> 15:38.000 If you have comments on today's show, please email the host directly, leave a comment on the website or record a follow up episode yourself. 15:38.000 --> 15:53.000 On this otherwise status, today's show is released on the creative comments, attribution, share a like, free.au license.